Download Chapter 3 Lecture Powerpoint.

CHAPTER 3 Marine Provinces

© 2011 Pearson Education, Inc.

Chapter Overview • The study of bathymetry charts ocean depths and ocean floor topography. • Echo sounding and satellites are efficient bathymetric tools. • Most ocean floor features are generated by plate tectonic processes.

© 2011 Pearson Education, Inc.

Bathymetry • Measures the vertical distance from the ocean surface to mountains, valleys, plains, and other sea floor features

© 2011 Pearson Education, Inc.

Measuring Bathymetry • Soundings – Poseidonus first sounding 85 B.C. – Line with heavy weight – Sounding lines used for 2000 years

• Unit of measure is a fathom – 1.8 meters (6 feet)

• First systematic measurements – HMS Challenger 1872 © 2011 Pearson Education, Inc.

Measuring Bathymetry • Echo Soundings – Echo sounder or fathometer – Reflection of sound signals – German ship Meteor identified mid-Atlantic ridge in 1925

• Lacks detail • May provide inaccurate view of sea floor

© 2011 Pearson Education, Inc.

Echo Sounding Record

© 2011 Pearson Education, Inc.

Measuring Bathymetry • Precision Depth Recorder (PDR) – 1950s – Focused high frequency sound beam – First reliable sea floor maps produced – Helped confirm sea floor spreading

© 2011 Pearson Education, Inc.

Measuring Bathymetry Modern Acoustic Instruments • Side scan sonar – GLORIA (Geological Long-range Inclined Acoustical instrument) – Sea MARC (Sea Mapping and Remote Characterization)

• Can be towed behind ship to provide very detailed bathymetric strip map • Multi-beam echo sounder – Seabeam © 2011 Pearson Education, Inc.

Side Scanning Sonar

© 2011 Pearson Education, Inc.

Sea Floor Mapping from Space • Uses satellite measurements • Measures sea floor features based on gravitational bulges in sea surface • Indirectly reveals bathymetry

© 2011 Pearson Education, Inc.

Measuring Bathymetry • Seismic Reflection Profiles – Air guns – Strong, low-frequency sounds – Details ocean structure beneath sea floor

© 2011 Pearson Education, Inc.

Seismic Reflection Profile

© 2011 Pearson Education, Inc.

Hypsographic Curve • Shows relationship between height of land and depth of ocean

© 2011 Pearson Education, Inc.

Hypsographic Curve • • • •

70.8% of Earth covered by oceans Average ocean depth is 3729 meters Average land elevation is 840 meters Uneven distribution of areas of different depths/elevations • Variations suggest plate tectonics at work

© 2011 Pearson Education, Inc.

Ocean Provinces Three Major Provinces • Continental margins – Shallow-water areas close to shore

• Deep-ocean basins – Deep-water areas farther from land

• Mid-ocean ridge – Submarine mountain range © 2011 Pearson Education, Inc.

Ocean Provinces

© 2011 Pearson Education, Inc.

Continental Margins • Passive or Active • Passive – Not close to any plate boundary – No major tectonic activity – Example: East coast of United States • Active – Associated with convergent or transform plate boundaries – Much tectonic activity © 2011 Pearson Education, Inc.

Active Continental Margins Convergent or Transform • Convergent Active Margin – Oceanic-continent convergent plate boundaries – Active continental volcanoes – Narrow shelf – Offshore trench – Example: Western South America © 2011 Pearson Education, Inc.

Active Continental Margins • Transform Continental Margin – Less common – Transform plate boundaries – Linear islands, banks, and deep basins close to shore – Example: Coastal California along San Andreas Fault

© 2011 Pearson Education, Inc.

Passive and Active Continental Margins

© 2011 Pearson Education, Inc.

Continental Margin Features • • • •

Continental shelf Shelf break Continental slope Continental rise

© 2011 Pearson Education, Inc.

Passive Continental Margin Features

© 2011 Pearson Education, Inc.

Continental Shelf • Flat zone from shore to shelf break – Shelf break is where marked increase in slope angle occurs

• Geologically part of continent • Average width is 70 km (43 miles) but can extend to 1500 km (930 miles) • Average depth of shelf break is 135 meters (443 feet) © 2011 Pearson Education, Inc.

Continental Shelf • The type of continetnal margin determines the shelf features. • Passive margins have wider shelves. • California’s transform active margin has a continental borderland.

© 2011 Pearson Education, Inc.

Continental Slope • Where deep ocean basins begin • Topography similar to land mountain ranges • Greater slope than continental shelf – Averages 4° but varies from 1–25° gradient

• Marked by submarine canyons

© 2011 Pearson Education, Inc.

Submarine Canyons • Narrow, deep, v-shaped in profile • Steep to overhanging walls • Extend to base of continental slope, 3500 meters (11,500 feet) below sea level. • Carved by turbidity currents

© 2011 Pearson Education, Inc.

Turbidity Currents • Underwater avalanches mixed with rocks and other debris • Sediment from continental shelf • Moves under influence of gravity • Sediments deposited at slope base © 2011 Pearson Education, Inc.

Continental Rise • Transition between continental crust and oceanic crust • Marked by turbidite deposits from turbidity currents • Graded bedding in turbidite deposits • Deposits generate deep-sea fans, or submarine fans • Distal ends of submarine fans becomes flat abyssal plains © 2011 Pearson Education, Inc.

Abyssal Plains • • • • •

Extend from base of continental rise Some of the deepest, flattest parts of Earth Suspension settling of very fine particles Sediments cover ocean crust irregularities Well-developed in Atlantic and Indian oceans

© 2011 Pearson Education, Inc.

Abyssal Plains

© 2011 Pearson Education, Inc.

Abyssal Plain Volcanic Peaks • Poke through sediment cover • Below sea level: – Seamounts, tablemounts, or guyots at least 1 km (0.6 mile) above sea floor – Abyssal hills or seaknolls are less than 1 km (0.6 mile) above sea floor

• Above sea level: – Volcanic islands © 2011 Pearson Education, Inc.

Ocean Trenches and Volcanic Arcs • Convergent margins generate ocean trenches. – Deepest part of oceans – Most in Pacific Ocean – Deepest trench – Mariana Trench at 11,022 meters (36,161 feet)

• Volcanic arc on nonsubducted ocean plate – May produce island arc, e.g., Japan

• Continental arc on land © 2011 Pearson Education, Inc.

Pacific Ring of Fire • Margins of Pacific Ocean • Majority of world’s active volcanoes and earthquakes • Marked by convergent boundaries

© 2011 Pearson Education, Inc.

Ocean Trenches and Ring of Fire

© 2011 Pearson Education, Inc.

Mid-Ocean Ridge • Longest mountain chain • On average, 2.5 km (1.5 miles) above surrounding sea floor • Wholly volcanic • Basaltic lava • Divergent plate boundary

© 2011 Pearson Education, Inc.

Mid-Ocean Ridge

© 2011 Pearson Education, Inc.

Mid-Ocean Ridge Features • Central rift valley downdropped by seafloor spreading – Fissures and faults in rift valley

• Seamounts – tall volcanoes • Pillow lava or pillow basalt – shapes formed when hot basaltic lava quickly cools

© 2011 Pearson Education, Inc.

Mid-Ocean Ridge Features Seamount

Pillow lava

© 2011 Pearson Education, Inc.

Mid-ocean Ridge Features Hydrothermal Vents • Sea floor hot springs • Foster unusual deep-ocean ecosystems able to survive without sunlight • Warm water vents – temperatures below 30°C (86°F) • White smokers – temperatures from 30–350°C (86–662°F) • Black smokers – temperatures above 350°C (662°F) © 2011 Pearson Education, Inc.

Hydrothermal Vents

© 2011 Pearson Education, Inc.

Fracture Zones and Transform Faults

© 2011 Pearson Education, Inc.

Transform Faults and Fracture Zones

© 2011 Pearson Education, Inc.

Oceanic Islands • Volcanic activity • Hotspots • Island arcs

© 2011 Pearson Education, Inc.

End of CHAPTER 3 Marine Provinces

© 2011 Pearson Education, Inc.